The invention relates to an apparatus and a method for monitoring the sealing web width of sealed package units in which products are packaged.
The products may be, for example, solid bodies, powders, granules, pastes or liquids. Such products are often packaged in sealed package units, in particular package units which are sealed in an airtight manner, in order to protect them from drying out or the ingress of moisture or else with regard to their sterility (contamination by micro-organisms). Typical products in the foodstuffs industry are mustard, mayonnaise or ketchup, and typical products in the pharmaceutical industry are tablets, sugar-coated tablets, skin gels or ointments.
In order to provide an understanding of the invention, packaging for moisture-pharmaceutical preparations in tablet form will be discussed by way of example below. Packaging means for moisture-sensitive pharmaceutical preparations in tablet form frequently uses foil and film which are sealed closed around the tablets. Each tablet is situated in a cell which is sealed in an airtight manner and is bounded all around on the outside by sealing seams. As a rule, a plurality of sealed tablets, for example two or four, are accommodated in one package unit in the form of a strip. Aluminum foil composites are particularly suitable as packaging material. In order to user the medicament, a strip unit with tablets is removed from the supply pack and the foil is tom open in the vicinity of a tablet, so that the tablet is available.
The sealing machine, in the production mode, provides the tablets such that they are sealed in in an airtight manner on a foil/film-type tablet carrier, in which each tablet is enclosed in a square by two longitudinal sealing webs and two transverse sealing webs. The longitudinal sealing webs are arranged parallel to the edges of the foil/film carrier and the transverse sealing webs are arranged perpendicularly thereto. During fabrication and automatic packaging, the tablet carrier is then cut off in each case in the region of a transverse sealing web, thereby producing smaller package units in strip form and each having two or four tablets, for example, which units are then packaged ready for sale in a box of 10 to 40 units.
The cutting-off apparatus that is usually employed is a rotating cutter roller, which places the separating cut as exactly as possible (xc2x11 mm) in the centre of a transverse sealing web. However it has been shown in operational practice that the tolerances of the sealing webs in the longitudinal direction are so large that it is not possible to achieve the accuracy demanded above. The inaccuracy in the separating cut has the effect that in unfavourable cases the transverse sealing web is cut at the edge or even outside the web width and the requisite reliably tight sealing-in of the tablets is no longer ensured. In these cases, air and moisture can penetrate and the storage life of the tablets is greatly reduced.
The invention is based on the object of monitoring the width of the transverse sealing web of the cut package units, and of generating a characteristic signal in the case of defective separating cuts. This signal can then be used for automatic ejection of the corresponding package unit.
This object is achieved according to the invention by means of a method which contains the following steps:
a. measured values corresponding to the distance from the scanned surface are acquired at a clock frequency proportional to the transport speed by two laser-optical sensors which are arranged opposite one another above and below the cut package units;
b. summation values are formed from the two measured values of the two sensors, the said measured values being recorded in the same clock cycle;
c. the number of successive summation values in which a predetermined reference value is exceeded or undershot is determined;
d. an output signal is generated if the number of summation values determined in c. falls below a predetermined critical value.
If a tablet strip is situated between the two sensors at the measurement instant, then the sum of the measured values of the two sensors (summation value) corresponds to the thickness of the tablet strip.
In the region of the gap between two package units, the laser-optical sensors measure distances from surfaces that are very far away. In comparison, the distances from these surfaces that are very far away differ by several orders of magnitude from the distances from a package unit passing through. To ensure that the uncontrolled large measured values of the sensors resulting from the distances from the remote surfaces are not processed further, these measured values in each sensor can be set to a predetermined, constant measured value.
The clock frequency may be generated by a clock frequency generator coupled to the drive shaft of the conveying device which transports the package units in strip form in a cyclic or continuous manner.
The laser-optical sensors are preferably colour-independent.
According to a preferred embodiment of the invention, the output signal triggers ejection of the corresponding package unit.
Furthermore, the invention relates to an apparatus for carrying out the method according to the invention. This apparatus comprises two laser-optical sensors, which are arranged opposite one another above and below the cut package units and whose measured values are acquired at a speed-proportional clock frequency, a clock frequency generator, which prescribes the clock frequency for acquiring the measured values, a matching unit, which forms the summation value from the two measured values of the sensors, the said measured values being measured in the same clock cycle, and the evaluation unit, which determines the number of summation values which lie above or below a reference value and generates an output signal if the number of summation values falls below a predetermined critical value.
The clock frequency generator is preferably coupled to the drive shaft of the conveying device which transports the package units in strip form in such a way that it generates a speed-proportional clock frequency.
In a preferred embodiment of the apparatus according to the invention, the sensors produce analogue measured values from which an analogue summation value results and the matching unit matches the analogue summation value to an analogue-to-digital converter (ADC) and generates a digital summation value which is processed further in the evaluation unit.
The measured values of the sensors which are characteristic of the region of the gap between two package units preferably assume a predetermined, constant quantity.
A holding-down device preferably fixes the cut package units on their support in the region of the laser-optical sensors.
In a preferred embodiment of the invention, an ejection unit is arranged downstream of the laser-optical sensors in the conveying direction, which ejection unit ejects the corresponding package unit when an output signal from the evaluation unit is received.
The following advantages are obtained with the invention:
Packaging with cutting errors can be identified automatically and reliably. It is possible to prevent such defective packaging units from being packed any further.
By precluding this source of defects, the requisite product storage life can be reliably adhered to. Subsequent checking that is otherwise necessary can be obviated.